1. Field of the Invention:
The present invention relates to a circuit for electric power source which may be applied to an equipment such as a copier which has loads such as a clutch, solenoid, high voltage unit, D.C. motor and a micro-computer on board.
2. Description of the Prior Art:
Generally, in an electrophotographic copier a variety of devices are arranged so as to carry out a series of copying processes. Of such devices, there are, for example, a paper feeding device to feed copy paper, a driving device to synchronously drive both a lamp-mirror of an optical scanning system and a photosensitive drum, a high voltage unit to supply a high voltage to the respective electrodes for charging, transferring and electrostatically separating operations, and the like. Inside said devices, there are provided mechanical parts such as a clutch, solenoid, D.C. motor, or an electric power source input section, and the input voltage of the order of several tens of volt must be applied in general in order to operate each.
Heretofore, for an input voltage fed to said mechanical parts, there has been used a stable voltage (such as a three-terminal regulator output or a switching regulator output) or an electric power source full-wave rectified by a diode bridge, for example, after a voltage of 100V A.C. is stepped-down by a transformer, with all the faults such as expensive costs and instability.
In the case of using a stabilized power source such as a three-terminal regulator and the like, a voltage not lower than a certain voltage is converted into heat which is consumed in order to stabilize the power source. Therefore the efficiency thereof is insufficient and a large capacity capacitor for a smoothing effect is required, so that the costs thereof have been relatively expensive. With the switching regulator as shown in FIG. 1, the circuit constitution has become complicated, so that the cost is seriously high.
Now, in the case of using an unstabilized full-wave rectified power source, the device can be simplified and economized in cost. However, they have the following problems:
(1) There is the different period of time (i.e., the response) to attain a required torque between the case of commencing to drive such mechanical parts at the neighborhood of the wave form of OV and the case at the neighborhood of the wave form of the peak, so that accurate control is impossible.
(2) Even if the wave form effective value is, say, 24V, the peak value thereof is of the order of 34V, so that the driving element such as a transistor or a thyristor must be selected having the absolute maximum rating with sufficient allowances and it is apprehended that the cost thereof may become expensive, and
(3) The voltage fluctuation of the power source for a copier affects directly such a device, so that the rotational rate of a D.C. motor fluctuates. To cope therewith, in a clutch and the like for example, there must be selected parts having enough torque with allowances to take said fluctuation into consideration.